Coating structure of a cnd coated cutting tool and method of manufacturing the same

Abstract

A coating structure and preparation method for a CVD coated cutting tool, relating to the field of coated cutting tool processing technology, is disclosed. The coating structure comprises a wear-resistant layer, a composite transition layer, and a thermal barrier layer arranged sequentially from the inside out. The wear-resistant layer is an MT-TiCN coating, and the thermal barrier layer is an α-Al₂O₃ coating. The composite transition layer comprises transition layers A1, A2, and A3 arranged sequentially from the inside out. Transition layer A1 is an MT-TiCN coating, and transition layer A2 is a Ti(C)₂ coating. x1 N y1 O z1 The coating, with transition layer A3 being (Ti) 1‑a Al a (C) x2 N y2 O z2 The acicular crystal structure of transition layer A3 and the introduction of Al provide optimal crystallographic orientation induction for the nucleation of α-Al2O3, which is key to achieving a high (006) texture. Transition layers A1 and A2, through progressive compositional adjustments, ensure bonding strength with the wear-resistant layer, effectively improving the cutting performance of the coated tools.

Description

Technical Field

[0001] This invention relates to the field of coated tool processing technology, and more specifically, to a coating structure for a CVD coated tool and its preparation method. Background Technology

[0002] Chemical vapor deposition (CVD) is a core technique for preparing coatings for cemented carbide cutting tools. The resulting multilayer composite coatings significantly improve the wear resistance, oxidation resistance, and service life of the tools, meeting the growing demands of modern manufacturing for high-speed, dry cutting. During high-speed cutting, the tool tip experiences extremely high temperatures; therefore, the excellent thermal stability of the coating is crucial to ensuring its performance. Since US Patent 7993742B2 disclosed an α-Al₂O₃ coating with a (006) texture, for nearly two decades, α-Al₂O₃ coatings with a high (006) texture have become the preferred choice for coated cutting tools used in high-end steel turning due to their superior thermal barrier properties.

[0003] The regulation of α-Al₂O₃ (006) texture has always been a research focus in this field. Currently, the mainstream methods focus on optimizing process parameters during the Al₂O₃ nucleation or growth stages to induce preferential growth of α-Al₂O₃, especially by controlling the partial pressure and ratio of H₂S and CO₂ (JP6955706B2, US9987687B2). Some studies have also attempted to influence texture evolution by controlling the oxidation process (US10865476B2) and the surface roughness of the matrix (US20220288697A1). However, there are still few studies on the inducing effect and regulation mechanism of different transition layer structures on α-Al₂O₃ (006) texture. In fact, the design and systematic research on the transition layer structure itself in China is also insufficient. While patent CN103171178B details the microstructure and mechanical properties of the transition layer, it lacks an exploration of its influence on the growth behavior of α-Al₂O₃ crystals, particularly its texture. Furthermore, the composition and structure of the transition layer are crucial factors affecting the bonding strength between α-Al₂O₃ and MT-TiCN. Summary of the Invention

[0004] The purpose of this invention is to provide a coating structure for CVD coated cutting tools and a method for preparing the coating structure. This coating structure, through its unique transition layer design, can enhance the α-Al2O3 (006) texture, thereby improving the cutting performance of the cutting tool.

[0005] The embodiments of the present invention are implemented as follows:

[0006] A coating structure for a CVD coated cutting tool includes a wear-resistant layer, a composite transition layer, and a thermal barrier layer arranged sequentially from the inside to the outside. The wear-resistant layer is an MT-TiCN coating, and the thermal barrier layer is an α-Al2O3 coating.

[0007] The composite transition layer comprises transition layer A1, transition layer A2, and transition layer A3 arranged sequentially from the inside out; transition layer A1 is an HT-TiCN coating; transition layer A2 is a Ti(C) coating. x1 N y1 O z1 The coating satisfies x1+y1+z1=1; the transition layer A3 is (Ti 1-a Al a (C) x2 N y2 O z2 The coating satisfies x² + y² + z² = 1.

[0008] A method for preparing the above-mentioned coating structure includes:

[0009] Transition layers A1, A2, A3, and a thermal barrier layer were sequentially deposited in the wear-resistant layer using a CVD method.

[0010] The beneficial effects of the embodiments of the present invention are:

[0011] This invention provides a coating structure for a CVD coated cutting tool, comprising a wear-resistant layer, a composite transition layer, and a thermal barrier layer arranged sequentially from the inside out. The wear-resistant layer is an MT-TiCN coating, and the thermal barrier layer is an α-Al₂O₃ coating. The composite transition layer comprises transition layers A1, A2, and A3 arranged sequentially from the inside out. Transition layer A1 is an HT-TiCN coating, and transition layer A2 is a Ti(C)₂ coating. x1 N y1 O z1 The coating, with transition layer A3 being (Ti) 1-a Al a (C) x2 N y2 O z2 The acicular crystal structure of transition layer A3 and the introduction of Al provide optimal crystallographic orientation induction for the nucleation of α-Al2O3, which is key to achieving a high (006) texture. Meanwhile, transition layers A1 and A2, through progressive compositional adjustments, ensure strong bonding with the wear-resistant layer, effectively improving the cutting performance of the coated tools. Attached Figure Description

[0012] To more clearly illustrate the technical solutions of the embodiments of the present invention, the accompanying drawings used in the embodiments will be briefly introduced below. It should be understood that the following drawings only show some embodiments of the present invention and should not be regarded as a limitation on the scope. For those skilled in the art, other related drawings can be obtained based on these drawings without creative effort.

[0013] Figure 1This is a scanning electron microscope image of the coating structure provided in Embodiment 1 of the present invention.

[0014] Figure 2 The XRD diffraction pattern of the coating structure provided in Embodiment 1 of the present invention;

[0015] Figure 3 The EBSD test results are for the coating structure provided in Embodiment 1 of the present invention;

[0016] Figure 4 The peeling test results of the coating structure provided in Embodiment 1 of the present invention before and after wet sandblasting (left figure is before wet sandblasting, right figure is after wet sandblasting).

[0017] Figure 5 The wear diagrams of the rake face (left) and flank face (right) of the CVD coated tool provided in Embodiment 1 of the present invention after the experiment with cutting parameter 2;

[0018] Figure 6 The images show the wear patterns of the rake face (left) and flank face (right) of the CVD coated tool provided in Comparative Example 3 of this invention after an experiment with cutting parameter 2. Detailed Implementation

[0019] To make the objectives, technical solutions, and advantages of the embodiments of the present invention clearer, the technical solutions in the embodiments of the present invention will be clearly and completely described below. Where specific conditions are not specified in the embodiments, conventional conditions or conditions recommended by the manufacturer shall apply. Reagents or instruments whose manufacturers are not specified are all conventional products that can be purchased commercially.

[0020] The coating structure and preparation method of a CVD coated tool according to an embodiment of the present invention will be described in detail below.

[0021] This invention provides a coating structure for a CVD coated cutting tool, which includes a wear-resistant layer, a composite transition layer, and a thermal barrier layer arranged sequentially from the inside to the outside. The wear-resistant layer is an MT-TiCN coating, and the thermal barrier layer is an α-Al2O3 coating.

[0022] The composite transition layer comprises transition layer A1, transition layer A2, and transition layer A3 arranged sequentially from the inside out; transition layer A1 is an HT-TiCN coating; transition layer A2 is a Ti(C) coating. x1 N y1 O z1 The coating satisfies x1+y1+z1=1; the transition layer A3 is (Ti 1-a Al a (C) x2 N y2 O z2 The coating satisfies x² + y² + z² = 1.

[0023] The wear-resistant layer and thermal barrier layer are existing known coating materials. The wear-resistant layer uses an MT-TiCN coating with a thickness of 2~12μm, preferably 4~10μm. It has high hardness and is the main structure that bears cutting loads and resists abrasive wear. It provides a solid and flat crystallographic substrate for the fine transition layer and thermal barrier layer above.

[0024] The thermal barrier layer is an α-Al₂O₃ coating with a thickness of 2–10 μm. It has extremely low thermal conductivity, effectively isolating the high temperatures generated during cutting and protecting the tool substrate. Simultaneously, its high hardness and good chemical stability also contribute to wear resistance and oxidation resistance.

[0025] In existing technologies, there are techniques for setting a transition layer between the wear-resistant layer and the thermal barrier layer. However, the transition layer in existing technologies does not consider its enhancement effect on the growth of the (006) texture. In this invention, the composite transition layer includes transition layers A1, A2, and A3 arranged sequentially from the inside to the outside, with an overall thickness of 0.3~1.5μm. The three transition layers each perform their respective functions and work synergistically to enhance the α-Al2O3 (006) texture while ensuring the bonding strength of the coating.

[0026] The transition layer A1 is an HT-TiCN coating, i.e., high-temperature deposited titanium carbonitride, with a thickness of 0.1~0.5μm. Compared with the MT-TiCN coating, it has a higher deposition temperature and a denser crystal structure. As the bottom layer of the composite transition layer, it has good structural continuity with the underlying MT-TiCN, and at the same time provides a higher temperature and more stable crystallization template for the transition layer A2.

[0027] Transition layer A2 is Ti(C) x1 N y1 O z1 The coating, namely oxygen-containing titanium carbonitride, is a composition gradient layer with a thickness of 0.1~0.6μm. The transition layer A2 serves as a composition and stress buffer layer. By introducing oxygen, a smooth composition gradient is established between the transition layer A1 (oxygen-free) and the transition layer A3 (high oxygen / aluminum), alleviating internal stress caused by abrupt changes in material properties and ensuring adhesion.

[0028] Transition layer A3 is (Ti 1-a Al a (C) x2 N y2 O z2The coating, a titanium-based compound containing aluminum and oxygen, has a thickness of 0.1–0.4 μm. It is a specially designed texture-inducing layer. Its needle-like crystal structure and the introduction of Al provide optimal crystallographic orientation induction for the nucleation of α-Al₂O₃, which is the decisive factor in achieving a high (006) texture. It directly "guides" the α-Al₂O₃ crystal above to preferentially grow along the (006) crystal plane with the best thermal barrier performance.

[0029] Through the transition and reinforcement effects of the composite transition layer, the (006) texture coefficient of α-Al2O3 in the thermal barrier layer can be greater than 5, which means that its crystal orientation is highly consistent, thus obtaining the best thermal barrier performance and stability.

[0030] It should be noted that the texture factor (TC) is calculated according to the Harris formula:

[0031] ,

[0032] In the formula

[0033] I ( hkl The X-ray diffraction intensity of the coating is denoted as . I 0 ( hkl ) is the X-ray diffraction intensity of the reference material. n The selected crystal planes are (012), (104), (110), (113), (116), (214) and (0012). The reference material in this invention is the PDF#00-010-0173 card.

[0034] Furthermore, the inner side of the wear-resistant layer is also provided with a bottom bonding layer and a visual identification layer. Both the bottom bonding layer and the visual identification layer are TiN coatings. The thickness of the bottom bonding layer is 0.1~0.5μm, and the thickness of the visual identification layer is 0.5~2μm. The bottom bonding layer is the first layer in direct contact with the cemented carbide substrate of the coated tool, and its main function is to enhance the adhesion between all subsequent coatings and the substrate. The visual identification layer has a certain degree of lubricity and is also the surface layer for subsequent wet blasting. Its golden color can also serve as a wear indicator layer, allowing for direct observation of the wear condition of the coated tool.

[0035] This invention also provides a method for preparing the above-mentioned coating structure, comprising:

[0036] Transition layers A1, A2, A3, and a thermal barrier layer were sequentially deposited in the wear-resistant layer using a CVD method.

[0037] Furthermore, the deposition conditions of transition layer A1 are as follows:

[0038] The temperature is 950~1050 ℃, the pressure is 150~180 mbar, and the reaction gases are 2.66 vol%~4.66 vol% CH4, 0.84 vol%~2.13 vol% TiCl4, 18.64 vol%~29.95 vol% N2 and the balance H2.

[0039] The depositional conditions of transition layer A2 are as follows:

[0040] The temperature is 950~1050 ℃, the pressure is 70~90 mbar, and the reaction gases are 1.08 vol%~1.76 vol% TiCl4, 1.07 vol%~1.78 vol% CO, 0.39 vol%~0.41 vol% CH3CN, 0 vol%~1.07 vol% HCl, 10.9 vol%~23.4 vol% N2 and the balance H2.

[0041] The depositional conditions of transition layer A3 are as follows:

[0042] The temperature is 950~1050 ℃, the pressure is 70~90 mbar, and the reaction gases are 1.28 vol%~1.72 vol% CH4, 1.40 vol%~1.58 vol% TiCl4, 2.72 vol%~2.92 vol% CO, 0.68 vol%~0.82 vol% AlCl3, 19.24 vol%~20.24 vol% N2 and the balance H2.

[0043] The composite transition layer formed under the above conditions not only has high bonding strength, but also has a better enhancement effect on the (006) texture coefficient of α-Al2O3.

[0044] Furthermore, the deposition conditions of the thermal barrier layer are as follows:

[0045] The thermal barrier layer is deposited at temperatures of 1000–1100 °C and pressures of 40–60 mbar; the deposition process is divided into a first nucleation stage, a second nucleation stage, and a growth stage.

[0046] The reaction gases in the first nucleation stage consist of 2.8 vol%–3.2 vol% CO2, 1.5 vol%–1.6 vol% HCl, 1.4 vol%–1.5 vol% AlCl3, and the balance H2. No H2S catalyst was used in this stage; without H2S catalysis, the nucleation rate of Al2O3 was relatively slow and controllable. By adjusting the ratio of AlCl3 to CO2, a very thin but densely packed and finely sized initial α-Al2O3 layer could be formed on the transition layer surface. This layer provided a uniform and continuous substrate for subsequent growth.

[0047] The reaction gases in the second nucleation stage consist of 4.7 vol%–4.9 vol% CO2, 0.42 vol%–0.44 vol% H2S, 2.65 vol%–2.75 vol% HCl, 1.04 vol%–1.08 vol% AlCl3, and the balance H2. This stage introduces the key catalyst H2S. Building upon the fine nuclei formed in the first nucleation stage, the introduction of H2S selectively promotes the preferential growth of nuclei with specific orientations while inhibiting other unfavorable orientations. Simultaneously, the increased CO2 concentration ensures a sufficient oxygen source, synergistically working with H2S to create the optimal thermodynamic and kinetic environment for the crystallization of α-Al2O3.

[0048] The reaction gases during the growth stage consist of 2.65 vol%–2.75 vol% CO2, 0.42 vol%–0.44 vol% H2S, 1.48 vol%–1.54 vol% CO, 1.48 vol%–1.54 vol% HCl, 1.52 vol%–1.56 vol% AlCl3, and the balance H2. CO is introduced during this stage; although a weak oxidizing agent, it allows for precise control of the "carbon activity" in the reaction zone. If the carbon activity is too low (strong oxidizing atmosphere), other metastable alumina (such as...) is easily formed. κ (Phase 1); if the carbon activity is too high, it will lead to carbide formation or a decrease in coating quality. The introduction of CO creates the ideal environment for the continuous growth of the thermodynamically stable α-Al2O3 phase, preventing the formation of harmful phases. At the same time, this stage reduces the amount of HCl and increases the amount of AlCl3 to improve deposition efficiency.

[0049] The features and performance of the present invention will be further described in detail below with reference to embodiments.

[0050] Example 1

[0051] This embodiment provides a coating structure for a CVD coated cutting tool, the preparation method of which includes:

[0052] S1. A TiN bottom bonding layer with a thickness of 0.4 μm is deposited on the surface of a cemented carbide substrate at a deposition temperature of 885 °C and a pressure of 200 mbar. The reaction gases are 36.11 vol% N2, 1.64 vol% TiCl4 and the balance H2.

[0053] S2. An 8 μm thick MT-TiCN wear-resistant layer is deposited on the surface of the bottom bonding layer at a deposition temperature of 885 °C and a pressure of 55 mbar. The reaction gases are 15.4 vol%~18.9 vol% N2, 2.34 vol%~2.57 vol% TiCl4, 0.77 vol%~0.87 vol% CH3CN and the balance H2.

[0054] S3. Sequentially deposit HT-TiCN transition layers Al and Ti(C) on the surface of the wear-resistant layer. x1 N y1 O z1 Transition layer A2 and (Ti 1- a Al a (C) x2 N y2 O z2 The transition layer A3 has thicknesses of 0.3 μm, 0.3 μm, and 0.1 μm, respectively.

[0055] The deposition conditions of transition layer A1 are as follows:

[0056] The temperature was 1000 ℃, the pressure was 160 mbar, and the reaction gases were 2.66 vol%~4 vol% CH4, 0.84 vol%~2.13 vol% TiCl4, 18.64 vol%~29.95 vol% N2 and the balance H2.

[0057] The depositional conditions of transition layer A2 are as follows:

[0058] The temperature was 1000 ℃, the pressure was 80 mbar, and the reaction gases were 1.08 vol%~1.76 vol% TiCl4, 1.07 vol%~1.78 vol% CO, 0.39 vol%~0.41 vol% CH3CN, 0 vol%~1.07 vol% HCl, 10.9 vol%~23.4 vol% N2 and the balance H2.

[0059] The depositional conditions of transition layer A3 are as follows:

[0060] The temperature was 1000 ℃, the pressure was 80 mbar, and the reaction gases were 1.28 vol%~1.72 vol% CH4, 1.40 vol%~1.58 vol% TiCl4, 2.72 vol%~2.92 vol% CO, 0.68 vol%~0.82 vol% AlCl3, 19.24 vol%~20.24 vol% N2 and the balance H2.

[0061] After deposition, the mixture was oxidized for 4 min in an atmosphere of 12.0 vol% CO, 4.0 vol% CO2, and the balance H2.

[0062] S4. A 5 μm thick thermal barrier layer α-Al₂O₃ was deposited on the surface of the composite transition layer at a temperature of 1010 °C and a pressure of 55 mbar. The deposition was carried out in three stages:

[0063] The reaction gases in the first nucleation stage consist of 2.97 vol% CO2, 1.56 vol% HCl, 1.41 vol% AlCl3, and the balance H2.

[0064] The reaction gases in the second nucleation stage consist of 4.82 vol% CO2, 0.43 vol% H2S, 2.68 vol% HCl, 1.07 vol% AlCl3, and the balance H2.

[0065] The reaction gases during the growth stage consist of 2.72 vol% CO2, 0.42 vol% H2S, 1.51 vol% CO, 1.51 vol% HCl, 1.56 vol% AlCl3, and the balance H2.

[0066] S5. A TiN appearance recognition layer with a thickness of 1 μm is deposited on the surface of the thermal barrier layer at a deposition temperature of 1010℃ and a pressure of 55 mbar. The reaction gases are 38.01 vol% N2, 2.26 vol% TiCl4 and the balance H2.

[0067] S6. After deposition, the sample is subjected to wet sandblasting for two-color treatment to remove surface microcracks and change the internal stress state of the coating for subsequent cutting experiments.

[0068] Figure 1 The cross-sectional morphology of the composite transition layer in this embodiment is shown under a scanning electron microscope. The needle-like structure of the transition layer A3 can be clearly seen, which is the key to enhancing the texture.

[0069] Examples 2-3

[0070] Examples 2 and 3 provide a coating structure for a CVD coated tool, the preparation method of which is basically the same as that of Example 1, the difference being that the deposition time of transition layers A1, A2, and A3 is different, resulting in different thicknesses of each layer. The differences in the thickness of the composite transition layers in Examples 1 to 3 are shown in Table 1.

[0071] Table 1. Comparison of composite transition layer parameters in Examples 1-3

[0072] Transition layer A1 (μm) Transition layer A2 (μm) Transition layer A3 (μm) Example 1 0.3 0.3 0.1 Example 2 0.2 0.4 0.1 Example 3 0.2 0.1 0.1

[0073] Comparative Examples 1-3

[0074] Comparative Examples 1-3 provide a coating structure for a CVD coated tool. The preparation method differs from that of Example 1 in that the process parameters of the composite transition layer are different. The specific process parameters are shown in Table 2.

[0075] Table 2. Process parameters of the depositional transition layer in Comparative Examples 1-3

[0076]

[0077] The structure and thickness of the transition layer in Comparative Examples 1 to 3 are shown in Table 3.

[0078] Table 3. Structure and thickness of the transition layer in Comparative Examples 1-3

[0079] Transition layer AlHT-TiCN (μm) Transition layer A2TiCNO (μm) Transition layer A3TiAlCNO (μm) Transition layer A4TiN (μm) Comparative Example 1 0.3 <0.1 Comparative Example 2 0.3 0.3 Comparative Example 3 0.2 0.6 0.1

[0080] It should be noted that, although Comparative Example 3 appears to have four layers deposited according to the process in Table 2, the second and third deposits are actually TiCNO coatings, only with different compositions. They cannot be distinguished from the structure, so they are all counted as transition layer A2 in Table 3.

[0081] Experimental Example 1

[0082] This experiment used CVD-coated cutting tools from Examples 1-3 and Comparative Examples 1-3. The texture growth of their α-Al₂O₃ coatings was detected by XRD diffraction. The XRD diffraction pattern of Example 1 is shown below. Figure 2 As shown in Table 4, the test results are as follows.

[0083] Table 4. Comparison of texture coefficients of Examples 1-3 and Comparative Examples 1-3

[0084] TC (012) TC (104) TC (110) TC (113) TC (116) TC (214) TC (0012) Example 1 0.07 0.14 0.10 0.03 0.09 0.08 6.49 Example 2 0.07 0.25 0.13 0.04 0.14 0.07 6.31 Example 3 0.15 0.23 0.13 0.07 0.12 0.11 6.19 Comparative Example 1 0.47 0.84 0.18 0.16 0.47 0.19 4.68 Comparative Example 2 0.17 1.98 0.19 0.21 1.17 0.23 3.05 Comparative Example 3 0.11 0.37 0.31 0.10 0.34 0.14 5.63

[0085] Among them, the (0012) crystal plane is a higher-order diffraction of the (006) crystal plane, and its intensity directly reflects the orientation degree of the (006) crystal plane. The higher the TC(0012) value, the stronger the (006) texture. As can be seen from Table 4, the TC(0012) values ​​of Examples 1 to 3 of the present invention are all greater than 6, while the TC values ​​of other crystal planes are much less than 1, indicating that the coating has a very strong (006) texture, the crystal growth resources are highly concentrated in the (006) direction, and the growth in other directions is strongly suppressed.

[0086] In contrast, although the coatings of Comparative Examples 1-3 exhibit a certain (006) orientation, their strength is much lower than that of the embodiments of the present invention, and their suppression of other crystal planes is relatively weak, resulting in a mixed or impure texture. Tables 3 and 4 show that Comparative Examples 1 and 2 were used to examine the effect of the absence of the transition layer A2 on the induction properties. It can be seen that the TC(0012) values ​​of both Comparative Examples 1 and 2 decreased to varying degrees. The absence of the transition layer A2 affects the formation of the needle-like structure of the transition layer A3, causing the originally regular and uniformly distributed needle-like structure to develop towards an incomplete crystal structure and disordered orientation. Furthermore, the effect becomes more pronounced as the thickness of the transition layer A3 increases (Comparative Example 1 vs. Comparative Example 2).

[0087] Comparative Example 3 uses transition layer A4 instead of transition layer A3 to examine the impact on induction performance when transition layer A3 is absent. Comparative Example 3 also exhibits a certain degree of induction effect without the needle-like structure of transition layer A3, but it does not reach the level of the embodiments of the present invention. Meanwhile, the (006) texture strength of Comparative Example 3 is significantly higher than that of Comparative Example 1, which also indirectly confirms the important role of transition layer A2.

[0088] Furthermore, the coating mechanism of Example 1 was subjected to EBSD testing, and the relevant IPF, pole figure, and inverse pole figure are as follows: Figure 3 As shown, EBSD, from both statistical and morphological perspectives, confirms that the α-Al2O3 coating of Example 1 possesses a (006) texture with extremely high strength and purity. This is corroborated by the XRD detection results.

[0089] Experimental Example 2

[0090] This experiment used CVD coated cutting tools from Examples 1-3 and Comparative Examples 1-3. Peeling tests (before wet sandblasting) were conducted on Examples 1-3 and Comparative Examples 1-3 in accordance with the national standard GB / T36591-2018 to evaluate the coating adhesion. The test results are shown in Table 5.

[0091] Table 5. Results of peeling tests for Examples 1-3 and Comparative Examples 1-3

[0092] sample Example 1 Example 2 Example 3 Comparative Example 1 Comparative Example 2 Comparative Example 3 Peeling grade (0, 0) (0, 1) (0, 0) (1, 2) (0, 1) (0, 0)

[0093] As can be seen from Table 5, the peeling grades of Examples 1 to 3 all reached (0, 0) or (0, 1), indicating that the bonding strength of their three-layer transition layer structure is very beneficial. However, in Comparative Example 1, which lacks transition layer A2 and has a very underdeveloped needle-like structure in A3, the transition layer A3 is so thin that it cannot even completely cover the underlying transition layer A1, resulting in the upper α-Al2O3 layer directly contacting the transition layer A1 in some areas. Due to the significant difference in lattice mismatch and thermal expansion coefficient between the transition layer A1 (HT-TiCN) and α-Al2O3, and the lack of compositional gradient buffering by the transition layer A2, this direct contact causes severe interfacial stress concentration, resulting in a significantly worse bonding strength and a peeling grade of (1, 2). In contrast, Comparative Example 2, due to its well-developed transition layer A3, although the needle-like structure is not as good as that of the example in terms of quality, resulting in a worse induction ability, is still thick enough to shield the transition layer A1 and form a mechanical interlocking effect with the upper α-Al2O3, so its overall bonding strength is acceptable.

[0094] Figure 4 The results of the peeling test of the coating structure of Example 1 before and after wet sandblasting are shown. As can be seen from the figure, the peeling level is 0 before and after sandblasting, indicating that the coating has good adhesion.

[0095] Experimental Example 3

[0096] This experiment uses CVD coated tools from Examples 1-3 and Comparative Examples 1-3 for cutting tests. The relevant cutting conditions and parameters are as follows:

[0097] Experimental machine tool: CK7525;

[0098] Processing material: 45 quenched and tempered steel;

[0099] Cooling method: dry cutting;

[0100] Cutting parameters 1: Vc=230m / min, ap=1.5mm, f=0.3mm / r, cutting time 13.3 min;

[0101] Cutting parameters 2: Vc=280m / min, ap=1.5mm, f=0.3mm / r, cutting time 6 min;

[0102] The wear value VB on the back face of each sample was statistically analyzed, and the results are shown in Table 6.

[0103] Table 6. Rake face wear values ​​VB of Examples 1-3 and Comparative Examples 1-3

[0104] Example 1 Example 2 Example 3 Comparative Example 1 Comparative Example 2 Comparative Example 3 Cutting parameter 1 0.156 0.188 0.205 0.412 0.535 0.33 Cutting parameter 2 0.223 0.286 0.288 Complete failure Complete failure 0.501

[0105] As shown in Table 6, the CVD coated tools of Examples 1-3 of this invention exhibit flank wear values ​​VB of 0.156-0.205 under moderately harsh conditions (cutting parameter 1). Under high-speed conditions (cutting parameter 2), the flank wear value VB increases slightly to 0.223-0.288, demonstrating excellent wear resistance.

[0106] In contrast, the wear values ​​(VB) on the flank face of Comparative Examples 1-3 under moderately harsh conditions reached over 0.33, with the highest reaching 0.535. Under high-speed conditions, complete failure even occurred, and the wear resistance was significantly inferior to that of the embodiments of the present invention.

[0107] Figure 5 The wear diagrams of the rake face (left) and flank face (right) of the CVD coated tool of Example 1 after the experiment with cutting parameter 2 are shown. Figure 6 The images show the wear patterns of the rake face (left) and flank face (right) of the CVD-coated tool in Comparative Example 3 after the experiment with cutting parameter 2. It is clearly visible from the images that the wear degree of the CVD-coated tool in Comparative Example 3 is significantly higher than that in Example 1.

[0108] In summary, this invention provides a coating structure for a CVD coated cutting tool, comprising a wear-resistant layer, a composite transition layer, and a thermal barrier layer arranged sequentially from the inside out. The wear-resistant layer is an MT-TiCN coating, and the thermal barrier layer is an α-Al₂O₃ coating. The composite transition layer comprises transition layers A1, A2, and A3 arranged sequentially from the inside out. Transition layer A1 is an HT-TiCN coating, and transition layer A2 is a Ti(C)₂ coating. x1 N y1 O z1 The coating, with transition layer A3 being (Ti) 1-a Al a (C) x2 N y2 O z2 The acicular crystal structure of transition layer A3 and the introduction of Al provide optimal crystallographic orientation induction for the nucleation of α-Al2O3, which is key to achieving a high (006) texture. Meanwhile, transition layers A1 and A2, through progressive compositional adjustments, ensure strong bonding with the wear-resistant layer, effectively improving the cutting performance of the coated tools.

[0109] The above description is merely a preferred embodiment of the present invention and is not intended to limit the invention. Various modifications and variations can be made to the present invention by those skilled in the art. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of the present invention should be included within the scope of protection of the present invention.

Claims

1. A coating structure for a CVD coated cutting tool, characterized in that, It includes a wear-resistant layer, a composite transition layer and a thermal barrier layer arranged sequentially from the inside to the outside. The wear-resistant layer is an MT-TiCN coating and the thermal barrier layer is an α-Al2O3 coating. The composite transition layer includes transition layer A1, transition layer A2, and transition layer A3 arranged sequentially from the inside to the outside; transition layer A1 is an HT-TiCN coating; transition layer A2 is a Ti(C) coating. x1 N y1 O z1 The coating satisfies x1+y1+z1=1; the transition layer A3 is (Ti 1-a Al a (C) x2 N y2 O z2 The coating satisfies x² + y² + z² = 1. The thickness of the wear-resistant layer is 2~12μm, the thickness of the composite transition layer is 0.3~1.5μm, and the thickness of the thermal barrier layer is 2~10μm; The thickness of the transition layer A1 is 0.1~0.5μm, the thickness of the transition layer A2 is 0.1~0.6μm, and the thickness of the transition layer A3 is 0.1~0.4μm.

2. The coating structure according to claim 1, characterized in that, The wear-resistant layer is further provided with a bottom bonding layer and an appearance identification layer on its inner side. Both the bottom bonding layer and the appearance identification layer are TiN coatings. The thickness of the bottom bonding layer is 0.1~0.5μm, and the thickness of the appearance identification layer is 0.5~2μm.

3. The coating structure according to claim 1, characterized in that, The (006) texture coefficient of α-Al2O3 in the thermal barrier layer is greater than 5.

4. A method for preparing a coating structure as described in any one of claims 1 to 3, comprising: The transition layer A1, the transition layer A2, the transition layer A3, and the thermal barrier layer are sequentially deposited on the wear-resistant layer using a CVD method.

5. The preparation method according to claim 4, characterized in that, The deposition conditions for the transition layer A1 are as follows: The temperature is 950~1050 ℃, the pressure is 150~180 mbar, and the reaction gases are 2.66 vol%~4.66 vol% CH4, 0.84 vol%~2.13 vol% TiCl4, 18.64 vol%~29.95 vol% N2 and the balance H2.

6. The preparation method according to claim 5, characterized in that, The deposition conditions for the transition layer A2 are as follows: The temperature is 950~1050 ℃, the pressure is 70~90 mbar, and the reaction gases are 1.08 vol%~1.76 vol% TiCl4, 1.07 vol%~1.78 vol% CO, 0.39 vol%~0.41 vol% CH3CN, 0 vol%~1.07 vol% HCl, 10.9 vol%~23.4 vol% N2 and the balance H2.

7. The preparation method according to claim 6, characterized in that, The deposition conditions for the transition layer A3 are as follows: The temperature is 950~1050 ℃, the pressure is 70~90 mbar, and the reaction gases are 1.28 vol%~1.72 vol% CH4, 1.40 vol%~1.58 vol% TiCl4, 2.72 vol%~2.92 vol% CO, 0.68 vol%~0.82 vol% AlCl3, 19.24 vol%~20.24 vol% N2 and the balance H2.

8. The preparation method according to claim 7, characterized in that, The thermal barrier layer was deposited at a temperature of 1000~1100 ℃ and a pressure of 40~60 mbar; the deposition process was divided into a first nucleation stage, a second nucleation stage and a growth stage. The reaction gases in the first nucleation stage consist of 2.8 vol%~3.2 vol% CO2, 1.5 vol%~1.6 vol% HCl, 1.4 vol%~1.5 vol% AlCl3, and the balance H2; The reaction gases in the second nucleation stage consist of 4.7 vol%~4.9 vol% CO2, 0.42 vol%~0.44 vol% H2S, 2.65 vol%~2.75 vol% HCl, 1.04 vol%~1.08 vol% AlCl3, and the balance H2; The reaction gases during the growth stage consist of 2.65 vol%~2.75 vol% CO2, 0.42 vol%~0.44 vol% H2S, 1.48 vol%~1.54 vol% CO, 1.48 vol%~1.54 vol% HCl, 1.52 vol%~1.56 vol% AlCl3, and the balance H2.

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